text:
How can I find the location and coverage of aviation VHF transmitters?
In the USA, is there a way to find locations of VHF transmitters that are used for air traffic communication, and the frequencies they transmit/receive on? There are some places (Northern Bay Area, CA) where I fly where I have good signal/communication with a Terminal Radar facility, but have trouble contacting area approach in the same area - especially when low (<2000ft AGL). The area is hilly.
I'm interesting in seeing range and altitude support for a given frequency (in a given area).

I'm not sure how you are going to get that information. VHF is line-of-sight and is affected by terrain. It doesn't really depend on the frequency, but the terrain between you and the transmitter and if the transmitter is shadowed by terrain.

@RonBeyer A given transmitter does not transmit all frequencies. Knowing the location of a transmitter (and potentially its altitude) will potentially help knowing what altitude to be at before making a call, given it's line of sight, and given that it's possible to see the height of hills in between a flight path and the transmitter. Hence the question.

I commute from KRDD to KCCR almost every week.  The RCO are located on a sectional (so you know the locations).  On Monday mornings it is not unusual for Oakland to ask people how well they hear various outlets.  I don't remember promises about radio coverage except for MEA/MCA on IFR sectionals.  Sorry.

You can probably assume, for purposes of estimating, that a VHF antenna is located on the airport and use the airport elevation + 50 or 100 feet. You can also find locations of RCO stations and the elevations at those places. Unfortunately I do not believe that there is a list of antenna locations with frequencies, altitudes/antenna heights, and transmitting power.

Looks like FAA used to publish this info but they discontinued it (security reasons?). This doesn't have frequencies, just locations.

This is a useful site (https://www.radioreference.com/apps/db/?rpt=6&aid=2236), and the locations of these match up with the RCO locations on the sectional . Seems Mt Tamalpais RCAG is the one that applies to my area. The list seems a little out of date, however, as the location of "Priest - RCAG" doesn't have anything on the sectional, or in Google Maps.

seems to be a map of RCOs and frequencies for Alaska, but navigating back through the hierarchy doesn't yield this info for the conterminous US states http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/systemops/fs/alaskan/alaska/rco/

@RonBeyer: (just an addition) "VHF is line-of-sight", that's true overall indeed. However on short distances like in the case here, diffraction and reflection can play an important role and make links possible using broken lines and multiple paths. Else in a city nobody would receive FM radio or aerial TV. On the other hand, the volume that must be kept clear is the innermost volume of the Fresnel zone, because energy propagation is not only along a line. Bottom line... it's a complex calculation!

An interesting tool for LOS and Fresnel zone calculation: Geocontext profiler. Exemple. Screenshot.

@TomMcW That's a useful reference... a Google search for just the lat/lon locations doesn't reveal any other sites with the same information. Do you know how this info was compiled?

@CJBS Not a clue. I just found it hunting around on Google. I had a list at one time of the RCAG sites for ZME that I think was FAA issue, but I think it was on my old cell phone that broke. I have a map somebody made of the ZKC sites. Once again, don't know how accurate. In a forum on that RadioReference.com site someone said the FAA didn't put it on the web any more but they have a CD-ROM of it. But it kind of sounded like they just don't give it to anybody that asks. I'll look for that forum entry because I think they had a link

@CJBS I found that forum entry. It's 10 years old and the links are all broken. It's referring to the ATA-100 and I'm not sure RCAG sites are even on that. You might comb through this and see what's there. It's a bunch of zip files so I don't know what it is,

@CJBS Apparently it is on there: "Open up AFF.txt located in the ZIP file most recently updated (20051222.zip in this case). It lists the lat/long coordinates of all the RCAG Sites, their cities, the airports they serve, etc. It also (very cool-ly) shows ARSR locations for the centers." Got that from here

This is a useful site for the Oakland (ZOA) Air Route Traffic Control Center (ARTCC), and the locations of these match up with the RCO locations on the sectional. It seems Mt Tamalpais RCAG is the one that applies to my area. The list seems a little out of date, however, as the location of "Priest - RCAG" doesn't have anything on the sectional, or in Google Maps.
Further, there is an FAA site depicting RCOs and frequencies for Alaska.

Upper VHF is essentially line of sight it is affected and reflected by both to Terrain and by building structures it will Imperfectly penetrate concrete and steel structures. It doesn't have much over the horizon capability.
UHF has better building Penetration, but no over the horizon capabilities.
Range for both is affected by three things 1)Antenna Type/height of the source and its 2)Power and 3)receiver location and orientation.
Under specific Atmospheric conditions, typically a temperature inversion, Tropospheric ducting can occur where RF is reflected further than its normal transmission range and achieve significant over the horizon capabilities. Conceivably this can disrupt local operations.
Essentially the higher you go in Frequency the more line of sight the signal is. Also more power is needed to maintain an equivalent range or the more sensitive a receiver needs to be.
Also sheets of metal will affect all frequency ranges somewhat. This is why the antenna needs to be outside the aircraft or vehicle.

Whilst this is useful background information on VHF transmissions (+1), the question is with regard to where transmitter locations are. As mentioned in the question, in a given location there are some facilities that I can communicate with easily, while others require being quite high to avoid signal obstruction from hills. Hence wanting a map of frequency/facility transmitter locations.

@cjbs if I didn't already see it in the below answer the location to the radio beacons are actually marked on your sectional map where they are. The actual transmitters for The Voice Communications are going to be located someplace on the airport property and that would be where you would determine your line of sight from. You would want to look for a few masts with vertical antennas. Separated by 30-40 feet.

@cjbs because the frequency ranges are close enough you could probably use any applications for amateur radio 2m(144mhz) propagation mapping for the 120mhz air band. The one thing I've learned from all of my other RF experience however is that any mapping application is of limited use and probably wouldn't tell you anything you haven't figured out by flying around in the area.

@Rowan_Hawkins - this might be true of airports, but that's not my problem. My problem is mostly with approach control. That's certainly not on the sectional - the dark magenta box I'm seeing says "CTC NORCAL APP WITHIN 20 NM ON 127.0 298.95"; no transmitter info included ...   https://skyvector.com/?ll=37.8182462196385,-122.14169311167971&chart=301&zoom=2

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How are Landing Fees Collected?
Some airports (mostly busy Class B airports from what I gather) have a landing fee. For example, in the Airport Facility Directory for San Francisco, there is a section under "AIRPORT REMARKS" that says "Ldg fee." In a Summary of Airport Charges for San Francisco airport, this fee is listed as at least $190 for Fixed-wing GA aircraft! There is no mention in this document about how the fee is collected, however.
How is this fee collected?

Won't answer because I cant for the US. But in the UK at small airfields it's usually just the guy sitting in the hut (tower!)

@Jamiec And we even have a specific sign (Black 'C' on a yellow background) for the location that visiting pilots should head to upon landing.

@Dan that sounds like a taxiway marker for taxiway "Charlie".

@CJBS I guess so, though it's a lot more obvious in reality http://ukga.com/images/content/image31589.jpg

@Jamiec Chaper 6 Page 5 of CAP637 (https://www.caa.co.uk/docs/33/CAP637%20Visual%20Aids%20Handbook.pdf)

@Dan I get'cha!

@Dan haha, yeah thats definitely not taxiway charlie.

Answered for large airports

This depends on the airport but at KPNE where I used to fly there was a $5 landing fee (paid to the city of Philadelphia) that was collected at the FBO (where I rented the plane from) when I paid for the rental. I think if you do not pass through an FBO they will hunt the tail number down and send a bill to the party that has the aircraft registered. Its tough to fly into an airport and not pass through the FBO (unless you are just doing touch and goes). I would assume that for commercial traffic the airline/owning body pays and may even be billed by the airport monthly but I don't know the specifics I only know what I have seen for GA traffic.
If you are curious you can check out the Philadelphia Airport (KPHL and KPNE) legislation here which outlines the various fess and collection mechanisms the city imparts. Keep in mind these are city owned airports, see section V for details on collection but in short,

Section V Part d
Non-tenant Air Carriers and Operators not providing adequate surety or security in form and amount satisfactory to the Department of Commerce, to ensure payment of fees and charges, shall be required to pay all incurred fees and charges prior to aircraft departure.

For the point of contrast lets take a small privately owned airport here in the US, Solberg Airport in NJ has "ramp fees" for parking and the such, but like most small airports like this, these fees are waved with the purchase of fuel (usually at least some minimum amount). There would be no way to avoid paying (well Im sure there is) since usually the only way off the tarmac is through the FBO.

I've flown into hundreds of airports in the US and they pretty much all work this way.  The FBO collects the fee (along with their own fees).  A few airports (like KMIA) also have a GC center that is run by the airport which you have to go to if you don't go to an FBO, and they can contact the tower to deny takeoff clearance if you don't visit them first.

@Lnafziger So what happens if it's a touch-n-go? Or is this just impractical given that it's typically such busy airports probably wouldn't allow this in the first place?

KPNE does allow them (load permitting) and remember you entered with a hail that included your tail number, they can find you pretty easily. I believe if you are inbound for some touch and goes then depart they will send you a bill.

@CJBS If you are asking about MIA, during the first time that you visit they get your billing information, so it doesn't matter anymore.  I'm not sure that they will let you do on if you haven't visited before though.

Two additional ways:

A little metal box with a slot at the top where your expected to shove some dollar bills in
Some airports collect landing fees by sending you a bill to the address in the FAA database.

What's a "losing" fee?

It's the fee you "lose" when landing at an airport. ;)

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What should I expect for an unannounced GA visit for touch-n-gos at San Jose?
I understand that KSJC is a busy airport. I have done touch'n'gos at Oakland (also a busy Class C airport), but they have three dedicated runways for GA aircraft.
There is nothing about which runway is preferred for GA operations at SJC in the Airport Facility Directory notes.
What should I expect if planning an unannounced trip to SJC (arriving from the north/north-east)? Are touch-n-goes tolerated (i.e. staying in the pattern)? Which runway should I expect to be directed to? Is there anything else I should know?
I'm looking for local knowledge from someone with experience flying in the area, for example "GA operations are usually conducted on 30L, as the air carrier terminal is on the the other runway, and transient parking is adjacent to this runway" [I'm not sure this is the case, this is just an example of the type of information I'm looking for].

I have flown several times to SJC for touch and goes. I have always been on the weekends, and probably in the afternoons. It is a lot of fun, especially because the runways are so long for a small plane. I think I’ve been three times, and each time they have accommodated me on 30L. The wind is almost always favoring the 30 runways, and I don’t remember ever being cleared for 30R.
They will occasionally make you circle briefly before entering the C. They will also sometimes make you extend for a pretty long pattern to the SE if they have a big fella cleared for 30R. All the big commercial jets seem to be sent to 30R, and it is small GA jets that use 30L.
I have only done touch and goes, as I wanted to get out of the way quickly. But I get the impression that the tower is happy to accommodate as long as they’re not too busy. My instructor told me that they sometimes will say ‘no’ if they are busy, especially during the morning push, but I have no experience of that.
Have fun! There’s a beautiful 787 that is often at the terminal, keep an eye out for it!

When circling to the south east, is this within the Class C, or south east of RHV's Class D?

KSJC is a towered airport so you are at the discretion of the controller as to what runway you will be instructed to use as well as if touch and go's will be permitted at the time. This may be load dependent when you arrive. I would expect either runway and it all depends who is about to depart when you arrive.

While a typical pattern is the norm at a towered field it should be noted the controller may extend a leg or two to make room for other traffic. It should also be noted that according to the AFD 30R and and 12R have Right Traffic while the other runways will have left traffic so you should be alert of the pattern you are flying depending on the runway you are inbound for.
Since this airport is with in class C airspace (from the surface) you will also need to contact the appropriate controller to enter the airspace.
You should always get a flight brief before heading out to ensure that there are no active Notams or information you may need about the airport.

One small clarification: your wording implies that "cleared for the option" and "cleared for touch and go" are the same thing, but they aren't. Being cleared for the option includes a touch and go, but being cleared for a touch and go doesn't include any other option.

very true, ill clarify

I did two touch'n'goes there on the weekend. Beforehand, I reviewed the airspace on the way in, and also called SJC tower, and spoke to a manager there, who advised that they'd usually try and accommodate at least one touch'n'go. I approached from the NE Bay (KCCR). Tower and approach want to make sure that approaching flights remain well clear of the busy Reid Hillview airport KRHV, which has a Class D top of 2000'.
I did a touch'n'go on 30L, then asked for another touch'n'go, which was granted. Advised of wake turbulance due to another takeoff on 30R (and relatively calm winds), I asked for an extended downwind, and was given instead a right 360, which I did. I also advised that I wished to depart back to KCCR, and was advised to fly heading 020 after take-off, which I did. This was to avoid the SDO Class B, and also to get me out of the way of a waiting jet behind me.
The controllers were helpful and friendly. Try it!
See the recorded route (which doesn't show the 360 well on the downwind).

SJC 30L is typically used for most arrivals & GA departures, while 30R is typically used for airline departures.  If no airline jets are about to depart, tower typically offers airline arrivals a side-step to 30R for landing.  In a typical operation, I'd anticipate getting 30L for GA touch & go's, with cautions as noted about wake turbulence from larger aircraft.

Nice, @RalphJ... now that you mention it, upon closer inspection of my photo, there are many more tyre touch-down marks on 30L compared to 30R...

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Does altitude influence the flight range of an engine driven aircraft?
I'm reading a chapter about flight performance during the cruise phase and the influence of altitude.
My book (Aerodynamica, prestatieleer en vliegtuigtechniek by Bas Vrijhof on page 155, written in Dutch) describes the following:

Naarmate de hoogte toeneemt, neemt de luchtdichheid af. De afnemende
  luchtdichtheid heeft een effect op het benodigde vermogen, en dus op
  de prestaties. Om bij een lagere luchtdichtheid te vliegen is meer
  vermogen nodig. Om bij een lagere luchtdichtheid voldoende lift te
  houden moet de TAS toenemen, dat kost vermogen.

Translated to English:

Airdensity decreases with altitude. A decrement in airdensity influences flight performance. To fly at a lower airdensity more engine power is needed. To maintain enough lift at lower airdensity the TAS needs to increase, this comes with the cost of engine power.

This is totally clear to me. Then the book says.

Endurance...
  Meer vermogen betekent een hogere brandstofverbruik. De endurance neemt daarom af.

Translated:

Endurance (amount of fuel per hour), more engine power means a higher fuel consumption. The endurance decreases with an increase in engine power.

Again, this is also clear to me.

Range...
  De range verandert niet bij toenemende hoogte. De range is niet afhankelijk van de vlieghoogte. Wel neemt de Vmax range toe als de hoogte toeneemt.

Translated:

Range (maximum flight distance, amount of fuel per km) doesn't change with an increase in altitude. However, the Vmax range increases with an increase in altitude.

The last sentence is confusing me.
Because my instincts say that a higher fuel consumption comes with a shorter flight distance. So my question is:
Is it really true that the altitude doesn't influence the flight range? Does the book has an error?

@ymb1 Correct me if I'm wrong. Flying higher means a shorter air time, and an increase in Vmax range. So, if I would fly with the Vmax range at a high altitude, then the max. air-time would be shorter compared to lower altitudes. But, flying with the Vmax range at relatively high altitudes means that the aircraft is able to cover the range / distance in a shorter time. So, the range doesn't change with altitude. So, the statement the book made is true.

Your book may not be wrong, but it is misleading, because the answers depend on the the aircraft type, and the type of engine. (piston, turboprop, turbojet, turbofan)
In general:
All aircraft have the best range at higher altitudes.
Piston powered aircraft have the best endurance at low atitude.
Jet powered aircraft have the best endurance at their optimum altitude. (not too low and not too high)

May I know why a piston powered aircraft has the best endurance at low altitude?

Maximum endurance is attained at minimum power setting and minimum speed for level flight. (low speed means less parasite drag) Any increase in altitude means a higher true airspeed for flight, and more parasitic drag. Piston engines are efficient at low altitudes even while operating at low power and RPM. Jet engines are optimized for high altitude by design and are not efficient at low altitudes.

"All aircraft have the best range at higher altitudes." What about balloons?

@AnonymousPhysicist The context of this question is aircraft-performance. Balloons are not aircrafts. Please stay on topic.

@MikeSowsun Isn't the efficiency of Piston engines also much more dependent on the density of the air? Both in terms of maximizing combustion and for cooling the engine.

@Julian Balloons are aircraft.  https://www.faa.gov/aircraft/air_cert/design_approvals/balloons/

@AnonymousPhysicist Ok a balloon is an aircraft, my bad. I edited the question title.

Jet engines can make the same horsepower/thrust at basically all altitudes due to their compressors, thus the same fuel burn - this lets them take advantage of the less dense air/less drag at higher altitudes, and perhaps take advantage of jet stream tail winds.  Well, maybe not the same, see here for more
How does turbojet thrust change with altitude?
Smaller planes can be equipped with turbochargers, or turbonormalizers, to make sealevel horsepower at higher altitudes and also take advantage of the thinner air.
Non-turbo engines like mine and most small planes are limited to leaning the mixture to keep the engine from running rich/wasting fuel as (generally) climb above 3000 feet. We can't get fully as high to the thinnest air, but we're also burning less fuel once cruise altitude is reached.

@ymb1 Is the lower thrust value at higher altitudes compensated for by the less dense air? I get the feeling that you don't need as much force to move an airplane at 30,000 versus sea level.

I think you can say "the lower thrust value at higher altitudes is caused  by the less dense air".

any aircraft has an optimal altitude for cruising. account for burn at takeoff and landing, then the cruising altitude is the one minimizing the costs. since combustible is the main cost, then is easy to determine which altitude is the economical one, even customized for the trip length and wind direction. however, for practical reasons and separation of air corridors, the economical altitude also depends on imposed constraints related to air traffic.
for distances of less than 1000km, the 6000m 675km/h turboprops of small capacity are the most economical. embraer and bombardier are flying those routes.
for longer distances, the 11000m 980km/h large airliners are the most economical.
for planetary distances, the largest airships are the most economical. the altitude is limited to 11000m.

Can you please add some sources?  This looks like a good answer in the making.

I’m sorry, I don’t have sources. Is what I’ve learned in pilot ground school

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Why is the Boeing 747-300 not in service anymore?
Doing a little doodling on flightradar24.com and Wikipedia, I saw that all the versions on the Boeing 747 except for the -300 version are used. Why is the Boeing 747-300 not used even though it is newer than the -100, -200, and SP versions?

The 747-300 was somewhat of a cross between -200 and SP. The -300 was almost same as the -200 except for the increased length of the hump. The -300 was never a success and was soon overshadowed by the -400.
The 747SP was the result of a requirement for longer range aircraft. Boeing engineers basically cut around 47' from the 747 fuselage in SP. However, by the time it flew for the first time, commercial air travel had changed (in no small part due to the high oil prices) and the model never sold as much as Boeing had hoped. However, when it was observed that there were no adverse effects when the rear of the cockpit lined up with the front of the wing, Boeing introduced the 747-300 with increased length of the hump with little else in terms of major change from -200.
However, just two years after -300 was introduced, Boeing introduced the -400, which was a significant improvement- it eliminated the flight engineer, increased range among others, while retaining the -300's hump (which meant more economy seats). 747-400 is the most successful model of the series, with more than 690 orders. Most airlines jumped straight to the -400, effectively killing the -300.
Actually, the 747-200 production (with over 390 made) ended after the -300 version (of which only 81 were made). So they are more of contemporaries.
Also, it'll be a stretch to call that the older 747 versions are still in passenger service. 747-100 is not flown with passengers anymore, current operations of 747SP hardly qualify as passenger service and the most successful of these, the 747-200s are also being slowly phased out, if you discount the VC-25s flying around with US President (which are slated to be replaced by 747-8s).

And, yes, it is quite the stretch to say that the pre -400 747s are still in passenger service. Most airlines retired them long ago. Indeed, many airlines are now retiring the -400s. Delta plans to have all of theirs retired by 2017, for example. Sadly, they're replacing them with twins and not 747-8s. Aside from perhaps their charter fleets (on which I have no experience,) those 14 seats upstairs on the 747s are the best seats on Delta's entire fleet, IMO. It feels like a private jet (at least until you walk down stairs and see the other 362 passengers.)

Just to add a little detail to the already good @aeroalias answer, former 742 operators also had the option to stretch the upper deck of their planes, as reported here: http://www.airlinereporter.com/2012/02/an-inside-look-at-the-boeing-747-stretched-upper-deck-sud/

and keep in mind that some operators that had both internally referred to their -300s as -200. KLM did so for example, after stretching the upper decks on their -200s. Unless you were an aviation nut and knew which specific registrations belonged to -300s you'd never know they operated both.


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What is the fundamental physics behind L/D decreasing as AoA increases beyond the optimal point?
Why does lift over drag decrease with AoA past the optimum AoA?  Is it because the backwards vector for a given lift force on the wing is now larger for a given air particle compared to lower AoA?
For a single air particle interacting with the wing at higher vs lower AoA does the higher AoA cause a larger change in the velocity of the air particle?
Are there other factors involved?

I guess you wanted to ask why lift goes up past the optimum AoA. Lift over drag will already be at its maximum at the optimum AoA.

The fundamental reason is that at high enough AoA, the lift becomes zero -- certainly no later than an AoA of 90°! At that point L/D is zero (there'll be lots of drag). So somewhere between 0° and 90° there will be an AoA with the highest L/D, and that is by definition the optimum AoA. Slightly beyond that angle there's nothing for the L/D to do except decrease, because if it didn't, the angle we're beyond wouldn't be the optimum.
Now if you were asking why that particular angle is optimal for a given airfoil, we would have to go into aerodynamics and boundary layers and whatnot. It's not merely about what happens to the molecules that (try to) hit the underside of the wing, but at least as much about how well the molecules above the wing can be convinced not to hit it.
Note that above the optimal AoA, until the critical (stall) angle, the lift generated still increases with increasing AoA -- it's just that in this range drag increases faster than the lift does.

I like this explanation and haven't seen it before.  Somewhere between 0 and 90 really gets the point across.

I don't think its true, but your explaination by itself doesn't show that there is only one point on the L/D curve where lift is maximum. Nor does it show that it is not linear. Either of these would mean that there is no single maximum.

@rbp: Yes, there could be more than one local optimum. But the curve can't be linear, because at (somewhere near) both 0° and 90° the lift will be zero with nonzero drag (and thus L/D=0), and if we call it a wing at all there must be an angle where it delivers positive lift (and thus positive L/D). In theory there could in an interval with exactly constant L/D, but such a degenerate case does not arise in practice. Change the Reynolds number by 0.01 and you'd miss it.

As I said, i don't think its true, but i think you might want to say something about the kind and order of the function you're describing.

Local speed at low angle of attack
At low angle of attack, the oncoming air hits the airfoil right at the tip of the leading edge. There is not much of curvature to negotiate before the long stretch with little curvature behind the nose follows. In order to change its flow path quickly, the air molecule must flow in a high pressure gradient, and this gradient accelerates it not only sideways, but also in flow direction. Consequently, high curvature areas see high local flow speed. (I explained the physics in a very simple way; if you want to know more, please read this).

Local speed at high angle of attack
With increasing angle of attack, the suction area over the airfoil needs to become stronger to force the airflow to follow the contour. Consequently, more of the oncoming flow is sucked over the wing, and the stagnation point shifts downwards on the airfoil's nose. Now the particles which hit the nose just above the stagnation point have to negotiate most of the nose's curvature, which needs more acceleration. This creates a suction peak in the flow around the nose and high local flow speed on the top side.
The flow over the bottom of the airfoil, however, will be decelerated near the stagnation point and see only little acceleration while it flows towards the trailing edge. See below for a plot of the inviscid pressure distribution. The pressure coefficient $c_p$ correlates with speed, and $c_p = 0$ means that local speed equals the flight speed of the airfoil. Negative values denote suction, and local speeds in excess of flight speed, whereas positive values of $c_p$ indicate slower speeds. Note that the y-axis is plotted reversed, with decreasing values up.

A high local speed will also cause high local friction. Also, the long pressure rise on the upper side at high angle of attack needs more energy from the outer flow to keep flow attached, so the boundary layer grows here and slows down more of the air than at low angle of attack (again, extremely simplified). Both effects mean that drag goes up at higher angle of attack.
If you increase the angle of attack further, the flow is not able to follow the upper contour and will separate. This causes the pressure rise to stop at the separation point, so downstream the pressure decreases. Since this part of the airfoil points slightly backwards, this local suction increase will drive up drag. This starts before stall and on a well-behaved airfoil the separation point will first be near the trailing edge and move upstream with increasing angle of attack. This means then drag will rise progressively with higher angle of attack. Since most of the flow is still attached, lift will still grow until stall.
Optimum angle of attack
The airfoil will be at its optimum angle of attack $\alpha$ with the best ratio of lift over drag $E_{opt}$ when the rate of lift increase with angle of attack equals the rate of drag increase times the optimum ratio of lift to drag. Once the local drag increase with angle of attack exceeds this value, the ratio of lift to drag decreases. Maybe this is easier to explain with a formula: $$E = \frac{L}{D}$$
To find the optimum we look at the point where the derivative of $E$ over $\alpha$ is 0:
$$\frac{\delta L}{\delta\alpha} = E_{opt} \cdot \frac{\delta D}{\delta\alpha}$$
The rate of lift increase over angle of attack is quite constant until stall. At low angle of attack drag decreases with increasing $\alpha$ until the minimum drag point is reached. Then drag goes up slowly, so the ratio of lift to drag still grows. At one point both grow such that their ratio will not change much, and once the rate of drag increase grows even higher, the ratio will drop again. This all happens before stall.

I think you were asking this question related to wing physics and not to airfoil physics. Here comes the physics of induced drag. I will try to simplify the explanation.
As you might know, the upper surface of the wing has lower pressure and the lower part of the wing has higher pressure. This is what is producing lift.
But... what about the tip of wing? Both sides are in contact so they should be at the same pressure?
So, we have a lower surface of the wing with higher pressure and the tip with "normal pressure", so, naturally in the lower surface the air will try to go from the root to the tip.
On the upper surface the situation is the opposity, the root will have lower pressure and the tip higher, so the air will try to go from the tip to the root.
As in the tip both sides are connected, the air will try to scape from the lower to the upper level (that's why there are wing tips). And that's why the tip vortexes are created with the typical pictures
Ok, now let's talk about drag. Drag is actually "any energy we are losing just because we fly" (ok, is a simplification but allows me to explain the next step). So, the airplane is losing energy and gives it to the air to create the tip vortex. The bigger the tip vortex the more energy is lost.
So, know coming to the question, why efficiency (L/D) decreases? So, as the angle of attack increases the lift increases linearly (proportional to the increase of the angle), however, the energy lost in the tip vortex (that is a component of drag) increases quadratically (proportional to the square of the angle of attack), that means that the drag is increasing more quickly (but starting at a lower level) that lift.
(lift grows, but drag grows proportionally faster)
So, we reach a point where the increase of drag makes the efficiency starting to decrease. That point can be calculated with the formula provided in the previous post.
Notice that the physics of the wing is more complicated as there are other drag components also interacting with the wing. It is also true that "infinite" wings have a maximum L/D, but there is a different mechanism in place.

At higher AOA, flow is separated, consequently Stall happens. Due to stall, Lift decreased and Drag increased, so L/D decreased.

For a typical wing, as the AoA increases, L/D has already been decreasing long before the stall angle is reached. Other answers assumed (correctly, I think) that the "optimum" angle in the question is the angle of maximum L/D, not the stall angle.

authors: استثنائيه لن اتكرر


text:
Why don't aeroplanes use propellers with more blades like the intake on a fanjet?
The air intake on a fanjet typically has many small angled blades. A wind pump in an American film might have many broad slatted blades. My desk fan has 3 very large scooping blades and seems quite effective.
It seems to me that if each blade provides thrust, the more blades you have, the more thrust you might expect. It also seems to me that a propeller with more blades could be smaller and turn more slowly, potentially avoiding going supersonic while providing the same level of thrust.
I ask because I'm building a drone and considering using six small multibladed props.
What are the downsides of adding more blades to propellers?

each blade also has it's own drag

Related question about propeller design.

@ratchetfreak Not only drag, but also weight. And the closer they are to each other, the less thrust they provide.

Not sure which windmills "on an American farm" you're referring to, but the new ones they're putting up on wind farms here in the midwest have 3 very long, slender blades.

@FreeMan He means a windpump usually placed over a well to pump water

@FreeMan - yes, I mean a wind pump. The classic one you see in films with many slatted vanes. I'm from the UK.

@superluminary Just as an FYI, films are about the only places you'll still see those. The one in the image linked above, according to the description, is from the year 1880. Most parts of the U.S. do, in fact, have electricity and running water these days. :)

On the continuum between propeller-driven and turbofan-driven craft is the "propfan."  I found some reading on the design considerations of those illuminating with respect to this question.

The Supermarine Spitfire went through about 24 Marks in WWII. As the Merlin (later Griffon) engine evolved, the prop went through 2, 3, 4, 5, and 6 blades.

Every blade will create its own boundary layer and its own vortex sheet. It is more efficient to use fewer blades with deeper chord, because the forward part of a boundary layer contributes most to friction drag.
To keep the lift coefficient on the propeller blade sections in a reasonable range (0.6 to 1.0) for efficiency means that blade chord will be reduced, which will make them less stiff. Again, it will be better to reduce blade count to arrive at a more viable design. All the thrust the propeller creates is pulling on those skinny blades, and they must be strong enough to withstand this force.
Only when the propeller disc loading increases do more blades begin to make sense:
 When engine power increases, the propeller disc area should also grow, but this growth is limited by the resulting speed of the blade tips. Once the flow speed there becomes supersonic, the drag at this section of the blade increases without a corresponding increase in thrust. To avoid that the next best option is to increase the solidity ratio of the propeller, called also the activity ratio.
Make no mistake, this is bad for efficiency. But if there is enough power available, adding more blades is the best way out.
You are right, a lower prop speed allows to increase its diameter, but while tip speed will drop by less than the reduction in prop speed (after all, flight speed should not change), the available thrust from this propeller will drop by the square of the speed reduction, since thrust is proportional to the dynamic pressure on the blades. And thrust you get only from the circumferential fraction of the local speed at the blade; flight speed does not count here and does not help to mitigate the reduction.

If I understand, the fan in a turbo-fan engine works because the nacelle impacts the airflow around the edges of the fan, is that correct?

Indeed, the most "efficient" propeller is probably a one-bladed propeller - but efficiency doesn't propel aircraft, thrust does.

So are you in effect saying that a blade will provide thrust if it is moving relative to the air aound it. Adding more blades will swirl the air around in the propeller disk, which means that each blade will be moving less quickly relative to the air around it?

@superluminary: No, the speed around each blade will not change. But more blades will operate at a lower lift coefficient, creating more friction (= torque) for the same lift (= thrust). It is like adding a second wing to an airplane which should still weigh as much and fly as fast as before.

@FreeMan: The engine fairing improves efficiency for highly loaded props (= fans) and helps to equalize flow speed over the fan's operating conditions. But thrust is created on the surface of the fan blades by the pressure difference between the two sides of the blade. The fan would still work without the nacelle, but not as well.

@voretaq7: The motivation for this particular prop was the smaller cutout in the glider fuselage for the retractable engine. But you are right in principle, and some designs have been tested, but so far the regular application of single bladed props has not happened.

@PeterKämpf Yeah that happens to be my go-to single-bladed prop picture. There are a couple of counterweighted prop photos on the front of "normal" airplanes, but those offend my delicate aesthetic sensibilities to look at :-)

@voretaq7: Looks like an amputee. Appalling!

My hunch was that using more blades would mean that each blade could be much less sturdy and therefore lighter. Perhaps the entire prop could be cheap plastic rather than metal or wood. The loss if a single blade would not be catastrophic. Am I way out here?

@superluminary: Don't underestimate the forces pulling on those blades. In a turbofan there is easily a pressure difference of one bar between the forward and aft side of the fan. Newer fans are indeed made of plastic, but the expensive carbon fiber-epoxy sort. Also, all the thrust a propeller creates is pulling at those thin blades. They need to be strong so they don't tear off.


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Does the co-pilot still remain in control of the plane if an engine fails during takeoff?
If an engine fails after $V_1$, how long does the copilot remain in control if he was the pilot flying? What is prioritized before the captain taking control of the aircraft?

The operating procedures for the four airlines I worked for (2 commuters and two 747 carriers) all called for the flying pilot (which would be the first officer if it was their leg) to retain control of the airplane until all relevant checklists had been accomplished.
That said, it is, of course, the captain's prerogative to take control at any point. That would, I think, be very unwise to do in the case of an engine failure during takeoff unless the first officer was really screwing up.
The greater workload in the 747 during emergency/abnormal procedures lies with the non-flying pilot and the flight engineer (old 3 man cockpit 747-100s and -200s).
The recommended procedure at my last two airlines was, if the captain was flying at the time of the failure, to hand control to the first officer after all relevant checklists had been completed, to thus enable the captain to give his full attention to how best to proceed.
My personal and observational experience is that there is little difference between captains and first officers at the 747 level insofar as control manipulation during go/no go situations on the runway in simulators. In fact, I could point you to an accident resulting in the total loss of a 747 when the flying pilot was the Captain, and he elected to abort 30 knots after $V_1$, thus insuring the aircraft would leave the runway.

In airline operations, both pilots are trained to handle engine failures at any point during the flight, including during the takeoff.
As far as who actually flies when it happens, it is a matter of the airlines SOP's and could be different from airline to airline.  In general it is safer for whoever is flying when the engine fails to continue rather than attempting to transfer the controls.  After an engine failure during takeoff, the aircraft is in a relatively unstable condition which often needs high control forces and the person flying has already figured out how much control pressure is required to keep it flying like it is supposed to.
The captain is always the final authority when it comes to the safe operation of the flight though, so if he felt that it wasn't going well, he could take over at any point.  Many captains actually prefer to have the first officer fly during abnormal situations like this because they can then "oversee" more effectively without having to focus so much on actually flying the airplane.


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Is it possible that derated thrust takeoffs are safer than normal takeoffs?
The reason for my arguments here are (assuming that you have sufficient runway distance):
That with less thrust, less force should also be required to hold the aircraft as desired, and possibly the aircraft should be easier to control and fly when the engine fails than if it does so with the thrust set to full blast.
An engine event, such as a bird strike, might (?) be less likely to have catastrophic consequences for e.g. the turbine blades when they are not running at full thrust and their design limits.
Never having actually commanded an aircraft, are any of these ideas correct?

The problem I see with that is with less thrust, you will not attain takeoff speed quickly; you will have less power when just off the ground; and you will climb more slowly. Thus, if there is a failure on takeoff, you are closer to the ground with much less time to react.

The reasons presented at ground school for the benefits of de-rated thrust takeoffs were twofold:

less chance of catastrophic engine failure during takeoff
less overall wear between overhauls

It is from this standpoint that reduced thrust takeoffs are safer.
As you point out, these are only authorized when the weights, temperature and runway length allow, but for the EMB-145 virtually every takeoff we did was eligible for reduced thrust.
You point about ease of control with an engine out is countered by engine out procedures which involve setting max thrust on the remaining engine (for two-engine ops).  During takeoff roll in the EMB-145XR, this puts the other engine at 117% power.  With the exception of flying near $V_{MC}$ (for light twins) the extra thrust is a benefit and not a hindrance to control and if this is at or after $V_1$ you'll want the thrust to go flying.
Your question about a bird strike is going to go one of two ways:

the bird hits the N1 fan and goes through the bypass ducting
the bird hits the N1 fan and is ingested into the N2 compressor stages

In either scenario a reduced thrust vs full thrust takeoff is not going to make a huge difference, but scenario 2 will be far more destructive to the engine than scenario 1.

ok, thanks for the clarification :) was wondering about the control since i saw a clip on youtube with some pretty strong rudder input when one of the engines blew, but of course the aircraft has been designed to be able to handle it so should not be a problem.
(ps. i think another advantage might be a little less noise pollution?)

With less thrust on takeoff, the plane will climb more slowly, keeping the aircraft closer to the ground for a longer time.  So the noise footprint (smaller due to the reduced thrust takeoff) will cover a larger area as the slowly climbing airliner drags the footprint over more territory.  So it is not a given that "noise pollution" will be less.

An airline policy of doing reduced thrust takeoffs is considered to improve safety in the longer term by reducing the probability of an engine failure, due to reduced cumulative wear on the engines and reduced engine stress during each takeoff.
The primary motivation for reduced thrust takeoffs however is cost. Engine life can be significantly extended by use of this policy. What "kills" an engine is peak engine temperature (EGT or ITT). Each degree of thrust reduction through assumed temperature method or derated takeoff makes a meaningful difference in peak EGT for that takeoff, and leads to a large cost saving in the long term.
Doing a reduced thrust takeoff does not reduce your safety margin in the event of an engine failure, since the engine-out takeoff profile will be calculated for that thrust value, ensuring that safe obstacle clearance will exist for each segment of the profile. In addition to this however, maximum thrust is still available to the pilot at any point should he desire more thrust. Additionally, from a handling point of view an engine failure will be easier to control at a lower takeoff power setting than at maximum takeoff thrust.
Reduced thrust takeoffs is the industry standard and I would estimate that less than one in a thousand of the takeoffs I do is with maximum thrust. In fact we have to write it up in the technical log every time a maximum thrust takeoff is done.


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Can anyone identify this aircraft in the AMARG area of Davis Monthan?
Anyone has an idea what this thing in AMARG area of Davis Monthan could be?

Googlemaps link: https://www.google.com/maps/@32.1512545,-110.843407,25m/data=!3m1!1e3?hl=en

Another angle, from here.

Problem solved, a close friend of mine pointed to these two very interesting articles on the topic:
http://foxtrotalpha.jalopnik.com/a-new-angle-on-this-shadowy-stealth-f-a-18-hornet-conce-1727910676
http://aviationweek.com/awin/super-hornet-stealth-test-rig-seen

please post here the relevant informations, links can rot and this answer would then be useless.

D/V until/unless you edit your answer to include enough information within the answer itself. FYI, at my current location, I cannot go to the jalopnik site, as it has issues, and the aviationweek site is a paywall.


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What does a dollar sign mean in a METAR?
Look at this METAR:
KLOU 151553Z 21005KT 10SM CLR 13/M01 A3044 RMK AO2 SLP309 T01281011 $
What does the dollar sign mean?

It means that they need to spend some money to fix whatever is broke on the automated reporting station!

@RalphJ That's actually a great mnemonic!

A maintenance indicator sign, $, is included when an ASOS/AWSS (Automated Surface Observing System / Automated Weather Sensor System) detects that maintenance is needed on the system.

Reference: http://www.faa.gov/documentLibrary/media/Order/JO%207900.5C.pdf
Or if you need an easy way to remember it, courtesy of the awesome Ralph J:

It means that they need to spend some money to fix whatever is broke on the automated reporting station!

To improve the answer, it would be nice if you could resolve the ASOS and AWSS abbreviations, please.

ASOS = Automated Surface Observing System; AWSS = Automated Weather Sensor System. These are nicely described at https://en.wikipedia.org/wiki/Automated_airport_weather_station

Another appropriate reference for this would be the "Aviation Weather Services" advisory circular.


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What is this white rectangle painted on runway 23 at KCRW?
(Related to this question.)
Runway 23 at Charleston, WV (KCRW) appears to have a (roughly) 500' x 50' white rectangle painted on the touchdown zone (I've added red arrows pointing at each end of the box):

Source: Google Maps
What is it used for?

In the remarks for runway 23, it identifies it as a "Military Assault Landing Zone" and non-standard markings (RMK-ANG: RWY 23 NONSTANDARD MARKINGS/MILITARY ASSAULT LANDING ZONE). I can't find any information about exactly what they mean though, it is a pretty ambiguous search.

@RonBeyer: It appears to be for C-17 to practice short landings (and be certified for), to be ready for really short strips in isolated areas. Same marking and skidmarks (source)

@mins I know the C-17 is capable of short-field landings, but I would be incredibly impressed if it could land in 500', maybe that is just a touchdown zone marking? The "image" you posted doesn't show a whole lot, would be nice to see the video itself...

@RonBeyer: Click on "source" for the video. I believe the pilot ignores the standard ICAO markings and uses the lines to assess the approach angle and land (the video is not very informative).

Interesting tidbit. KCRW is also the call letters for the public radio station out of Santa Monica CA (Los Angeles area).

Seems to be touchdown zone markings for assault landing practice by C-17's. For assault landings, the standard is to touch down in the first 500' of the Landing Zone (LZ), and to go around if your mains aren't on the ground by the 500' point. On a dirt LZ, there will typically be panels set out to mark the threshold, the 500' point, and the far threshold -- that way the combat control team which is marking the LZ doesn't have to put out lots of panels, but there are enough for the crew to get what they need. The 500' markings on the main runway would give enough information to the crew to simulate landing on an LZ, even though the actual runway is far longer & wider.
This frame below shows examples of C-130's practicing assault landings, and you can see orange panels at the threshold and 500' points in them:

Source: YouTube
Some places, KLRF (Little Rock Air Force Base) for example, had an actual 3500' long paved strip for crews to use for assault landing practice, with permanent markings at the threshold and 500' points (2013 imagery shown below):

Source: Google Earth
Most airports don't have the budget to create a separate runway for this specialized requirement, so some sort of markings on the main runway are used instead.

The amount of rubber on the tarmac in the KLRF landing zone is kind of impressive.


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Is there any obvious warning when auto-pilot is disengaged or when the mode changes?
Under the investigation section of the First Air Flight 6560 incident, it describes the catalyst for the accident:

The approach was entirely flown on autopilot, which was correctly set to capture the localizer signal and track along the runway centreline (VOR/LOC capture mode). However, an inadvertent movement of the control column by the captain during the turn onto the final approach track caused the autopilot to disengage from VOR/LOC mode and revert to maintaining the current heading, resulting in the aircraft rolling out to the right (east) of the runway centreline.

My question: Is there any obvious warning (on common commercial aircraft, i.e. 737, A320) when auto-pilot is disengaged or when the mode changes?
I would have expected there to be an audible notification, some flashing light or something to make it as apparent as possible that something has changed, if it's as easy to change as 'nudging the stick'.

@ymb1 Thanks, I did have a look at that question. But I would like to know specifically what the warnings are on a 737, A320 and why said warnings didn't prevent the above incident. If you think my question could be worded a bit better, please feel free to edit.

@JohnK please avoid answers in comments

It looks like the wording in the Wikipedia article is somewhat unfortunate, since (at least to me), the terms "disengage" and "mode change" are different, yet the Wikipedia article uses the term "disengage from VOR/LOC mode" to talk about a mode change. In particular, a disengagement will issue a warning, since it is not commanded by the pilot, but a mode change is commanded by the pilot, and it is usually not needed to warn the pilot about something they did themselves. The problem in this case, of course, is that the pilot did not notice that he commanded a mode change.

You asked about commercial aircraft in general, so I will give an answer from that point of view.

Is there any obvious warning when auto-pilot is disengaged?

Yes, both visually as flashing lights, and aurally. Furthermore, the lights and tone does not go away until a second confirmation is received from the pilot. For example, pushing the button on the yoke / stick once will disengage the autopilot but trigger the warning. A second click is needed to silence it.

Is there any obvious warning when mode changes?

It is not a warning, as mode changes are explicitly made by the pilot. I'd still consider it "obvious" because the active mode is shown right on top of the Primary Flight Display (the instrument you should spend most of the time on).

Picture: A/P disengage button on yoke, A/P disengage warning light and A/P mode indicator circled in red.
Image source https://www.team-bhp.com/forum/attachments/commercial-vehicles/1506426d1463061690-boeing-777-pilots-review-boeing777cockpit.jpg

So what happened on First Air Flight 6560? In this particular instance though, there are a few factors (in my opinion) that contributed to the crew not noticing the autopilot state:

The 737-200 is a rather old design. Compared to a modern cockpit where things are seen "at a glance", it requires more concentration to fly.
The 737 series have a rather unpopular feature called Control Wheel Steering (CWS). It allows the pilot to partially disengage one axis (pitch / roll) of the autopilot by moving the yoke in that axis only. On newer models, this feature is removed since very few pilots actually use it. On the Boeing 777 for example, such yoke movement would result in A/P disengagement and the trigger of the warnings I described.

Note that this incident is quite similar to the crash of Eastern Air Lines Flight 401, where the captain accidentally bumped the yoke, causing the autopilot to switch from altitude hold mode to CWS mode in pitch. The pilots failed to notice the change in time to avoid the crash.

Most autopilots feature both an aural warning siren or similar aural cue as well as visual cues on both autopilot units as well as cockpit displays, so there is a means to alert a flight crew of an autopilot disengagement.
As to changing autopilot modes, there a visual cues for this on autopilot units, flight displays and separate autopilot mode displays to allow a flight crew to visually verify when an autopilot is engaged.


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LPV/LP approach (RNAV with WAAS): What is actually the "channel number"?
Curious about the answer to this question: How may I verify WAAS channel number on G1000?, I just found that SBAS/WAAS use in aviation seems to be poorly explained.
In particular the WAAS "channel number" seems to suggest that some radio frequency is associated with a given WAAS approach.

(Image taken from the linked question)
I think the WAAS service is provided by only two geosynchronous satellites, each one broadcasting on the same frequency the corrections for the whole US area. So there is no need to tune the WAAS receiver based on the airport location, the runway number, or the LPV identifier.
So the question: Are these 3 informations strictly redundant (maybe not taking into account version numbers), and they exist only for triple-check purpose?

LPV approach name: RNAV (GPS) Y RWY 36L,
WAAS channel number: WAAS CH 56613,
WAAS approach ID (aka reference path identifier): W36A

Could you confirm that selecting any of these values on the avionics will only change what is retrieved from the local navigation database, and will not impact the GPS/WAAS data received?
Note: I could understand if the approach were LAAS/GBAS (local ground-based) instead of SBAS.

The channel number is one way of selecting or confirming the correct approach has been loaded.  It was the original intent to just type in the channel number to select the approach.  Avionics manufacturers didn't like that approach.

-1 you didn't seem to read the airman's information manual reference from the question you quoted which clearly explained the "channel number" meaning.

It was in 2 places, the link you found and listed was one: http://forums.jetcareers.com/threads/waas-approach-plate-channel-numbers.75299/  - and the comment I made to the question that initially prompted you to ask this one supplied the AIM reference too.  Maybe there is sufficient abiquity in the AIM that you still have it as a question. But heck, +1 for asking for clarity.

No one has this correct.  The channel is a legacy of how the LPV is encoded in the nav database.  The format used is the same as a GBAS approach where a local VHF transmitter was used to broadcast local diff GPS corrections for precision GPS approaches.  The avionic used to fly these approaches had a code selection window where you entered a channel number - the channel number being generated based in the VHF number.  When LPV came along they used the same format in the nav database as the GBAS approach but still needed a "channel" number even though there was no longer an associated VHF transmitter.  ICAO manages allocation of these codes (used to be the FAA).  So basically they are helpful to identify you have the correct approach but otherwise mean absolutely nothing.

Welcome George. This is the key element I was looking for. Based on your answer I was able to find other details, so I posted complementary elements.

Superb, you extra information has added to my knowledge base too.

@George Williams provides the key element to understand why unique channel numbers are used for procedures not requiring individual radio channels, this is why I selected his answer. I'm only providing complementary information I could find based on George's explanation.

The GNSS 5-digit channel number is a way to select an approach on avionics equipements.

Gables G7501-01 panel (dual channel) used on Boeing 737. Source
In addition of tuning the receiver, this can also recall the associated approach path from the navigation database. Because the channel number can be used to select an approach path, it must be uniquely defined.
It can also be related to radio frequency but hasn't to, so "channel" is actually misleading. The radio part doesn't come from the GNSS signal frequency which is well known by itself, but from the GNSS augmentation system. GNSS position is usually improved (augmented) by GNSS signal correction to reduce the delay introduced by atmospheric refraction.
There are multiple ways to evaluate the required correction, and to broadcast it to the users. Broadcasting encompasses using ground-based transmitters (e.g. DGPS, known in the US as LAAS, and by ICAO as GBAS) and satellite-based transmitters (e.g. WAAS and EGNOS, collectively known as SBAS).
GBAS correction
GBAS corrections are essentially for users in a small area around the evaluation station, and different VHF frequencies must be used to not interfere. Transmissions are known as VHF Data Broadcast (VDB).
The channel number is computed from the frequency used, and also from an index identifying the system to be accessed, either the reference path data selector (RPDS) or the reference station data selector (RSDS), which is usually 0. The channel number is determined using the formula: $\small 20,000 + 40 (f – 108.0) + 411s$, $\small f$ being the VDB frequency and $\small s$ being the index.
GBAS approaches have channel numbers between 20,001 and 39,999.
SBAS correction
SBAS corrections are related to a wide region, e.g. a sub-continent, transmitters are based on geo-synchronous satellites and broadcast on the same L1 frequency than the GNSS constellation. So their frequency is well-known and no channel is to be selected.
The key information, provided by @George Williams, is the channel number in GBAS procedures allowed avionics manufacturers to select the approach path in the FMS and the VFB frequency in the NAV receiver. SBAS channel numbers have been reused as selectors for the approach path.
Channels 40,000 to 99,999 are reserved for SBAS approaches. Numbers are allocated by ICAO. On the past FAA used to assign numbers for WAAS area and Eurocontrol for EGNOS area.
For GNSS approaches, the channel number is equivalent to the procedure ID (here W36A, W for WAAS). With two identifiers for the procedure, it is possible to confirm the correct procedure has been loaded into the FMS. It's equivalent to tuning an ILS and checking the morse identifier. Navigation systems are required to allow selection by either of the identifiers (source).

Good summary. If you look through RTCA DO-229 (Rev C was the standard at the time) there are 3 functional classes and 4 operational classes that the standard supports. The GBAS and WAAS approach IDs are necessary in most Class Beta 3/Gamma 4 systems to synchronize the FMS and MMR equipment. Most GA equipment is Class Gamma and everything is internal making the IDs redundant to the approach name. In newer transport cockpits, the integration level with the FMS hides most of the radio/approach tuning from the crew, but it still there and available.

The key thing to remember is the channel number and approach ID are given to the approach but are NOT linked to the version of the approach.  They do not indicate you can skip the cross checking of all the data in each approach.  It just means you are looking at the right page!

This pdf by Jeppesen provides the meaning:

WAAS Channel Number, unique to each airport, and  Reference Path
  Indicator (RPI), which is made up of the letter “W” plus two or  three
  characters representing the runway number.  These are shown in both
  the Briefing Strip (chart heading) and plan view.

So the Channel Number provides the airport, and the RPI provides the runway number as well as the specific procedure. The combination of the two of them provides a specific approach at a specific airport, in much the same way that the title of the procedure on the approach plate is only meaningful if you combine it with the airport identifier.
As far as what you need to select in a particular avionics package, that depends on the design, but you are correct that it doesn't affect how it processes the GPS / WAAS signals.

Why the two procedures on the linked question have a different channel number while they are for the same airport?

@mins Excellent question, I checked the most current version of the charts and they are different too.  Doesn't seem to be consistent with what Jeppesen says...


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Do any propellers/propfans use stator vanes? Why is this not a commonplace feature?
I understand that axial-flow turbine engines generally include stator vanes behind every(?) compressor and turbine stage. This makes quite intuitively sense, because without them the rotating blades would mostly swirl the air around through the engine, which would not only prevent the stages from properly transporting/compressing/expanding the air in axial direction, but also put useless rotational kinetic energy into that air. The latter is presumably also the reason why turbofans have such guide vanes behind the fan, too.
All of this applies just as well to unducted fans/propellers. Yet I've never seen stator blades behind an open propeller. There are contra-rotating coaxial propellers of course, the idea of which seems to be similar: get rid of the useless solenoidal air motion. But actively contra-rotating both props adds a lot of complexity, and seems somewhat unnecessary if the goal is mostly to remove large part of the swirling motion. Cancelling all torque is not necessary for a plane.
Especially, I would think stators could also be shaped to help retrieve some energy from the tip vortices like a duct does, without however interfering with the inflow that seems to be the reason why ducts make props inefficient at low speed.

Loss of propulsion efficiency is gained back with faster, lower drag, higher flying, and larger (less parasite drag per unit mass) aircraft.  The 747 is champ at 80 ton miles per gallon fuel, even though it burns 5 gallons of fuel per mile!

The stator is the wing right behind the propfan. The contra-rotating propellers are precisely there to remove swirl and reduce swirl-related losses and asymmetries. And the tip vortices will be there regardless.

@PeterKämpf but contra-rotation requires mechanically demanding gearing, unlike a stator. And, if tip vortices would be created by the prop but most of their energy (or even just some of it) recovered again by the stator, then this would be no problem.

You ran only recover swirl losses, but not the energy in the tip vortices.

@PeterKämpf well, a duct can do this. Why would it be impossible with cleverly designed vanes?

Really? Says who? The seller of the duct?

@PeterKämpf probably. ...Ok, I've just got this from The Internet™, like, Wikipedia “By reducing propeller blade tip losses, the ducted fan is more efficient” but anyway – if it doesn't address the tip issue, the what is the purpose of a duct?

The duct helps to straighten the flow and to give it a uniform and constant speed, independent of outer conditions (flight speed, angle of attack). And do you believe everything somebody on the Internet, or Wikipedia for that matter, has said? Yes, I am fully aware of the irony of this statement appearing here on the Internet.

Sure, the internet is always right, right? ...Seriously, part of why that makes sense to me is because it matches what you said variously about prop blade number: many blades are bad because of the tip vortices; yet ducted turbofans get away with lots of blades and still achieve reasonably good efficiency.

Quick answer is that it boils down to thrust vs drag.  Propellers create thrust as airfoils and mass movers, fans are less efficient mass movers that can move much more mass if sufficient power is available.  This is why fans are teamed with jet engines.  Brute force.
A stator will not benefit the more efficient propeller, but I would not wish to discourage research.
The "reason ducts make props" link provided above is outstanding in that it shows each more efficient propulsion method falling by the wayside as speed increases due to drag,
while the turbojet keeps improving.


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Can a pilot change out of uniform during breaks on a long flight?
How long is a pilot-in-command's break on ultra-, or long haul flights? Would they be required to keep the uniform on, or would they have the freedom to change out of uniform?
Related: How do pilots rest on long-haul flights?

The answer depends a lot on the jurisdiction and airline, but Yes, pilots can change out of uniform during breaks on long flights.
A 15 hour flight would have 4 pilots who are all in the flightdeck for takeoff and landing but then divide roughly 14 hours of cruising time into equal rest breaks.
Typically 2 pilots will be paired together and take breaks at the same time. At some airlines they would have 2 pilots take a 7 hour break and then switch off. At other airlines they  take two 3 1/2 hour breaks.
Each 2 person crew would be off the flight deck for half of the 14 hours spent at cruising altitude (15 hour flight) I find most crews prefer two shorter breaks as opposed to one long break. With a 3 person crew they would have each pilot take 1/3 of the cruising time as a break.
Most airlines operate with one main crew who does both the takeoff and Landing. This is because the second crew is generally less qualified. In some cases the "augment" pilots are only licensed to operate during the cruise portion of flight. Some airlines will operate with two fully qualified Captains and two fully qualifed First Officers and they can divide the takeoff and Landing between the two Crews.
Most pilots change out of uniform during their breaks. Some airlines require the pilots to wear their hat and tie when they leave the flight deck.  Others are much more relaxed.
I have seen pilots in T-shirts enter and exit for breaks.


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How to fly a parabolic arc?
The title says it all, how do you fly a parabolic arc? Me and my friend Ben, are starting a research lab. We want to learn how to fly a parabolic arc.

With what? Do you mean vertically, or laterally?

Have a flight instructor show you.  You don't need a G-meter - a 12" piece of yarn tied somewhere convenient inside the cockpit will do.

The Vomit Comet enters the procedure at 360 kts and pitches up to 46°. At the top of the arc they pitch down 46* and level off at the starting altitude. Repeat 30-40 times. https://www.nasa.gov/missions/research/kc135.html

It's quite simple; I used to do it with my children, although it was a very small arc. I'd put something small and light (so it wouldn' hurt anybody if it hit them) on the top of the glareshield. Then bring the nose up to an attitude that would stall it if you kept it there, but well before the stall, push over until whatever you put on the glareshield floats. It takes a bit of practice to keep it floated in the same position for a few seconds. As the nose comes down through level, pull the power. Then you need to stop the arc and start the nose up again well before you hit Vne.

@Terry Ever tried Bob Hoover's tea pouring trick?

@TomMcW No, I was never that good, not even close. There are those whose performance for whatever reason, natural ability, experience, whatever, is simply phenomenal. He was one.

Pull the nose up, take out a pencil and hold it in front of your face, and then let go of it and keep it floating in front of your face by judicious use of the throttle and stick (yoke).
Obviously, you will end up in a dive, and airspeed will increase dramatically. If you approach Vne, or if the throttle reaches idle to keep the pencil from moving forward in the cockpit, you need to stop and recover. The higher your nose, and airspeed, the longer you will be able to do this before the nose gets so low that you must grab the pencil and cease the maneuver, and recover from the dive to avoid over-speeding the aircraft.

Get lots of airspeed,pitch up within ac flight envelope limits and as you approach stall speed for your configuration, push forward so that 0 G is shown on the g meter, and keep it there.
As you come over the top pull out again within it's so you neo not exceed Vne,Vmo or Mmo or g limit's for your planes . A parabola for a few minutes or second depending on the plane.

A few minutes?!  Two minutes of zero G will have you go from sea level to FL580 and back, and requires an initial vertical speed of 115750 feet per minute (1140 knots)! I guess it depends indeed on the plane, but to stay realistic I would not go beyond half a minute.

If you consider the Virgin Galactic hybrid aircrfat, spaceship  as an extreme case, I believe that they are advertising 4 minutes of weightless ness, but I concede that most aircraft are limited to far less. I do it for several seconds weightless ness in a glider showing pupils how, even when flying below stall speed the aircraft is both controllable... If sluggish, and definitely not stalled.


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Is it possible to turn and safely land an aircraft with a malfunctioning rudder?
Is it possible to turn mid air, and land a jumbo Boeing 747, Airbus A380 or any aircraft if the vertical stabilator is jammed in a position that allows it to fly straight at cruise altitude and speed, assuming everything else works including the horizontal stabilators?

Related, Emergency Flight Control Using Only Engine Thrust. More recently Nasa wrapped up the related studies for using engine thrust to steer aircraft: Manual Manipulation of Engine Throttles
for Emergency Flight Control. See also Japan Airlines Flight 123 accident. Burcham and Fullerton are experts on this topic.

On the Bagdad A300 DHL incident, the crew were able to stabilize  and land its aircraft without rudder control (and without many other critical systems)

https://en.wikipedia.org/wiki/United_Airlines_Flight_232

See also Northwest 85.

If the rudder is jammed in the neutral position (as stated in your question), then landing is easy. You will just land using ordinary techniques. The plane may feel sloppy, and passengers sitting at the back will complain about feeling dizzy, but the aircraft is easily controllable and landing would not be any problem.
Now things are different when the rudder is jammed to one side, for example in American Airlines Flight 96. The crew faced major controlling issues with a full right rudder, engine failure and very high sink rate. But even then, the pilots managed to land successfully.

"Easy" is always relative, but I'd rather not have to land a tailwheel aircraft in a crosswind without any rudder authority :-)

Yes.  One does have to be careful in turns and do it gently but it can be done as this graphic example of a B-52H on a test flight demonstrates.

Honestly a rudder failure during cruise flight does not present a major risk but would have to be handled with additional precautions such as gradual, gentle turns at higher speeds and a reduced flap setting landing in the airplane.  Additional differential thrust using the engine thrust levers can compensate for some of the adverse yaw encountered at these times.  The yaw damper would have to be disengaged as well.


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Is it possible to reuse water extracted from the PACKs Water extractors?
During the Process inside of the Air Generation Unit (AGU) there is a water extractor behind the condenser separating the water from the air which will flow to the Re-Heater.
Is it posible to filter this water and re-use it for lavatory flush or hand wash water?
Since Humidity at FL300 is around 3%, is there even sufficient water being extracted to refill the tanks?

If you did reclaim it, I'm sure it would be fine to use as non-potable (term for water you don't drink). Whether or not it is worth the extra weight, cost, and maintenance is another matter though that I'm guessing the answer is  "not worth it" when you can just take a small tank of water with you.

Water comes from condensing water vapor present in the cabin, itself coming from human breathing and perspiration, and, for a small part, from atmosphere.
The question mentions an air generation unit which is an Airbus terminology, so let's go into the A380 air system:

A380 Engineering training, source (page 101)
The two green labels are my addition to show the extractor and a spray nozzle. Water separated by a cyclone in the extractor is sprayed into ram air just after the ram air inlet and before entering the heat exchangers of the air-cycle machines. Spraying water droplets creates evaporation, hence a temperature drop in the exchanger receiving fluid, increasing air exchanger capacity.
Bleed air from the engines/atmosphere is colder and dryer at high altitude. Air exchangers work better, but cabin atmosphere may be dry for human well being. A fraction of condensed water can be returned to conditioned air going to the cabin. This is done automatically by the air-conditioning system.
To answer your question: Water is already fully reused.


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How long does it take for a propeller engine to spool-up?
To build further upon the question Why does a turboprop lag?, the following:
Assuming a propeller engine is running in idle and the throttle lever is switched to full thrust instantaneously at t = 0 seconds. How long does it take before the propeller delivers full thrust?
Exact times for a specific engine or range/order of magnitude for a generic one would be appreciated

Piston-engines and turboprops have quite different dynamics, even if both use propellers. In which are you interested?

In my Cessna Cardinal, with 360 cubic inch (~5.9L) carburated engine, I push the throttle in and the response is immediate.  Just like stepping on the pedal in a car with a standard transmission because propeller RPM = engine RPM. I have a constant speed prop, with controllable pitch angle, so it sort of acts like a standard transmission, I can dial it to any 'gear' I want to. For take off and landing, the pitch is flattest, and most responsive. Just like in a car, I can dial the prop pitch flatter and add more throttle for a climb from level cruise, then when at altitude I can dial the prop pitch up and throttle back down for efficient cruising. In planes we generally don't go to full thrust instantaneously, that's rough on the engine, but smoothly push the throttle in, maybe 2-3 seconds from idle to full throttle.  During landing, sometimes a bit of throttle is added to arrest an increasing descent rate, and even that is applied smoothly, and rarely full throttle unless a go-around is needed.
This link shows how the oil pressure, springs, governor, and other bits are used to control the propeller pitch when the RPM has been selected.
http://www.boldmethod.com/learn-to-fly/aircraft-systems/how-a-constant-speed-prop-works/

That is awesome! +1

On my airplane's piston engine, 2-3 seconds to go from idle to redline on a "slam acceleration".  On a free turbine turboprop like a PT-6 where there is a separate gas generator and power turbine, that has to spool up from idle rpm, more than double that, say 5-7 seconds.  On the CF-34 turbofan used in the RJs, which I have personal experience with, and which is really just a fixed pitch free turbine turboprop, same same, 5-7 seconds. On a constant speed single spool turboprop like an Allison T56 (like in the Herc) which is always "spooled up", it'll be faster than a free turbine engine, so say in between the others.
With free turbine turboprops there is very little torque produced at idle and there is a lot of inertia to overcome.  You can start and run a PT-6 at idle while holding the propeller blade stationary (this is done sometimes, or at least used to be) and as long as you don't let it start to move, it only takes a firm grip on the blade to hold it there.  If you let it start to move torque builds rapidly and you have to let go and get out of the way.

Re "...2-3 seconds to go from idle to redline on a "slam acceleration"", that's assuming that the slam acceleration doesn't stall the engine.  In which case you'd better hope that you have enough altitude for the windmilling prop to restart the engine.

Not saying I do it, but any piston engine that is warmed up and has an accelerator pump in the carb will take rapid full throttle without stumbling, or something is wrong with it.  That is the point of accelerator pumps in carburetors.  I used to fly a Bowers Flybaby with a C-85 that DIDN'T have an accelerator pump and yes it would stumble with rapid throttle movement and you had to work the throttle like a 1st generation turbo jet.   "Slam acceleration" is actually a term used in turbojets when fuel controllers came out that allowed that sort of thing.

I've never taken the carb apart (carbs and I do not get along well), so I don't know whether that plane had an accelerator pump or not.  I only know what happened when I tried the "slam acceleration" once.  Ever since, I've always taken a second or two to go to full throttle.  (And turbojets are way out of my price range :-()

I agree but there are scenarios, like if you were to bounce on touchdown and find yourself 5 feet in the air with vanishing elevator authority and the only way to save it is a blast of power NOW, the normal gentleness goes out the window.  It won't damage an engine.  A chum crunched the nose and wrote off his Cardinal because he bounced and it started pitching over and couldn't bring himself to shove the throttle in fast enough to mitigate the situation.


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Is there statistical evidence of the benefits of CRM?
Seeing there's apparently now a consideration towards allowing single pilot commercial aircraft, I figured a fairly good counterpoint would be the benefits gained from crew resource management (which I've often seen pointed to as something that might have prevented earlier accidents).  Has any empirical evidence been published showing a clear reduction in accidents linked to the development of CRM?

The benefits gained from CRM are not really applicable to a single pilot situation although solo pilots can apply CRM Ideals in their own regard. This FAA study touches upon it well in this study (numbers provided in the figures on page 2 of the study)

Concern with the factors underlying these accidents led NASA
  researchers in the 1970s to conduct a series of interviews with line
  piLots to investigate their perceptions of aviation mishaps. Charles
  Billings, George Cooper, and John Lauber found that one mishap
  component consistently mentioned by pilots was inadequate training.
  Even more interesting, these researchers found that it was not
  technical training that these pilots felt they lacked, but training in
  leadership, communication, and crew management. In other words,
  traditional training had done an excellent job of imparting stick and
  rudder skills, but these pilots felt that they needed more training in
  crew oaordination. A subsequent analysis of jet transport accidents
  between 1968 and 1976 revealed more than 60 that involved problems
  with crew coordination and decision making (Cooper, White, & Lauber,
  1979).

CRM solves the problem of their being two brains in the cockpit. In other words one of the primary issues they found surrounding aviation incidents was the fact that there were two pilots who had communication troubles in the cockpit (with each other). In some regards a counter point can be made that removing the second pilot is safer by eliminating these possible issues. The study makes it clear that pilots across the board had satisfactory skills in identifying issues and flying the plane but encountered issues efficiently communicating the issues in the cockpit.
This is a tough topic as there are currently no single pilot certified airliners but there are some single pilot certified biz jets which makes that the next best place to look for info. A study was carried out on the difference in accident rates between single pilot and dual pilot situations which interestingly does not show a huge lean either way. The article does not talk about CRM but it could be a starting point for a meta study on CRM as it applies to that group of accidents.
On any note Captain Sullenberger makes it clear that good communication and CRM were key to the successful outcome of his ditching. There is a great interview where he talks about it here.
According to this paper poor CRM was one of the largest human factors in commercial accidents.

Within the preconditions level, CRM failures were associated with the
  largest percentage of accidents. Approximately 29% of all
  aircrew-related accidents were associated with at least one CRM
  failure.

I can't find a whole lot of direct evidence that CRM has made airplanes safer but the FAA tends to take the approach of identifying the large issues (of which CRM seems to be) then working the problem through training. It is far harder to isolate and subsequently measure human factors. Engines that stop running, brackets that fail, wires that short, etc. are much easier to study...

I can't find the article right now, but I read a report on the NTSB public inquiry with Sully. It implied that Sully's response to the question about CRM training went along with his general ability to say what the board liked to hear. Jeff Skiles, the first officer on the flight, is a much more straightforward person at the interviews. His response to the question as to whether CRM training affected the outcome his answer was a simple "No."


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About how many aborted takeoffs are there each year in commercial aviation?
Watching this sim of a 777 engine failure on takeoffs got me wondering about RTOs, and how often they occur.
The interest was further driven after reading a comment by N1755L that might underline jeopardy in the process:

If anything is to go wrong with the engines at close to the
  "not-enough-runway-left-to-safely-stop" point, the pilots have only
  10s of thousands of seconds of time to assess the situation and decide
  which decision is the correct one (attempt a stop, or continue the
  takeoff and get into the air).

Perhaps that's exaggeration.  And surely the majority of rejected takeoffs occur at safer speeds.  There appears to be a few similar questions about emergency landings, but nothing on RTOs?
I did find this article from an Aero (Boeing) magazine indicating:

Historically, the RTO maneuver occurs approximately once each 3,000 takeoffs. Because the industry now acknowledges that many RTOs are not reported, however, the actual number may be estimated at 1 in 2,000 takeoffs.

The article appears to rely on data a couple decades old.  But wondering if that would be a reasonable estimate today.  And, even better, if there's any data on the breakdown of RTOs by speed.
Whatever you've got will be of interest, whether the dataset is confined to specific countries or even airlines.

Tens of thousands of seconds? As in, several hours to a day?

Haha, yeah, sadly I read right through their (hopeful) typo :-p  We live in a weird era where we read almost expecting mistakes to fix in our mind.

As off today (March 21st), Aviation Herald lists 26 rejected take-offs, in 2018.
It's 110 days since the start of the year. So that's 110/365ths, or 0.31 of the year. So, the whole year will have 26/0.31, or about 84 rejected or aborted take-offs.
This assumes, all are reported in Aviation Herald, which is probably not true, so the real average number is likely to be higher. But that's a rough starting point, and probably the best estimate you will get.

Would probably be better to look at numbers over the last few years and averaging rather than extrapolating based on a few months.

@Notts90.  Completely agree, and probably should have suggested that. It would just be more time consuming than I wanted to spend, and in essence, my answer was to show a method they could pursue. But you're dead right. But one reason I didn't do that - I've never figured out how to get the second page of search results on AH, so if you have more than one page to count.. I can't!! Cheers.

I’d say RTO’s are such a minor situation that AVH probably only hears about a very small fraction of them.


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Why there so many pitch control surfaces on the Piaggio P180 Avanti?

Picture source.
I have seen that there is kind of sonic aircraft like B-1B Lancer that used elevator and canard or fins at the same time for pitch control. That quite understandable because it is fighter jet that required high precision control. There are another airplane that used canard but not elevator, like Tupelov Tu-144. But this Piaggio P180 Avanti is quite strange for me. It is equipped with elevator, canard, and also another additional device. I am not sure that propeller airplane needs what needed by the above B-1B Lancer.
Then my question are, what is that device (number 2 in the picture), what is that name, and what is that for? Are device number 2 and number 3 controllable?

Surface 2 is not for pitch but for directional stability and boundary layer control.

B-1 is not a "fighter".  Also, Tu-144 certainly did have elevators, in the form of elevons.  Its canard was probably not used as a primary pitch control.

What is that mean directional stability and boundary layer control? What is that boundary layer control and how it work?

@AirCraftLover, you may want to ask about boundary layers as a separate question in the Physics Stack Exchange.  It's part of "fluid flow" or "fluid dynamics."   Air flowing over the surfaces of an aircraft is an example of fluid flow; there are several different kinds of flow that occur near or next to a surface.  A boundary layer is when the flow changes from one type to another.  There's QUITE a bit of material to understand to answer the question "how it works."

OK, sure. Thanks.

Surface 1 is a  horizontal stabilizer with elevator, just the same as on any other aircraft with a T tail arrangement.
Surface 2 is called a rear strake or a tail fin. There is one on each side of the fuselage. They provide extra stability during operation at high angles of attack when the fuselage is disturbing the airflow to the vertical tail. They are not movable.
Surface 3 is a canard, providing extra lift. The canards on P.180 have a trailing edge flap. The flap is necessary to counteract the nose down trim of the flaps in the main wing. Without the canard flaps the elevator would not have sufficient authority to maintain adequate pitch control when full flaps are deployed on main wings.
Surfaces 1 and 3 have movable parts, but surface 1 is the only surface connected to pitch axis control of P.180.
Piaggio P.180 article on Flying magazine explaining design features (and a lot more).
Rear strakes- tail fins on Wikipedia

Is that the trailing edge flap of the canard also acting like wing for the nose?

The whole canard (with the flap) is acting as a wing for the nose, that's what canards do. The canard trailing edge flap is there to add lift when flaps on the main wings are extended. This keeps the aircraft in balance.

Why there so many pitch control surfaces on the Piaggio P180 Avanti?

You mark 3 surfaces, but only one is movable, i.e. there is only one pitch control surface on the P180, not "so many".

what is that device (number 2 in the picture), what is that name, and what is that for?

Don't know the name myself, but it is there to guide the airflow around the back of he fuselage.

Are device number 2 and number 3 controllable?

not for continuous pitch control, see above and Jpe61's answer

In my understanding, pitch control is to control the nose up and/or down. The canard has it trailing edge which also acts to up/down the nose. So, it is also pitch control. I don't think that it is used to roll, moreover to yaw. Isn't it?

@AirCraftLover that's why I specified continuous. a flap is a discrete control, in a completely different category from what usually people refer to as "pitch control". the latter is usually reserved for surfaces connected to the stick, that can command any angle between their extreme deflections. A flap is none of that.

No. 2 is a ventral strake and No. 3 is a canard.  Neither have actuated control surfaces on the P.180.  The ventral strakes are there to provide additional directional stability and the canards provide a more direct longitudinal balance and control, alleviating tailplane loads, and improving low speed handling.
The Avanti was built for speed (400 KTAS in a turboprop!) and quite a bit was sacrificed for that.  Note the thin, high aspect ratio wings and lifting body fuselage.

I believe the ventral strakes are also a remnant of the early (but short-lived) involvement of Learjet in the designing of the aircraft. Hence the same design can be found on the empennage of Learjets.

Ventral strakes are common a wide number of aircraft, not just Avantis and Learjets.  In truth, just like preset trim tabs or dorsal strakes they are additions made to correct undesirable performance eharacteristics found in development or flight test ie “Band-Aids for bad airplane design”.

Agreed, they certainly are found on many other aircraft, from the Q400 to light amphibians. But I think the design is clearly very similar to the Lear. Anyway, the band-aid analogy is a good one, which why the Beech 1900D is covered in strakes and other 'aero-band-aids'.

There is really some useful information in all answers. Two design choices really make me wonder how hard engineers worked to create that aircraft.
First; ventral strakes or tail fins. They are canted 45 degrees. Which means they  provide both pitch and directional stability. I also think they provide little bit of dihedral effect. Actually that maybe the main reason looking at straight mid-body wings and rectangular shape of engines. I’m sure they suffered from roll instability at the beginning. Canted ventral fins looks like a quick aerodynamic band-aid.
Second the front wings (as company calls them, not canards). It really wouldn’t make sense if they were really fixed small wings in front. They would make aircraft unstable in pitch. As the AOA increases lift of those front wings would increase also and aircraft would want to pitch up more and go out of control.

The truth is as @Jpe61 mentioned in his comment and as you can see at the beginning of that video they have trailing edge control surfaces. Looking at the location of wings and engines I think they suffered from aft CG problem and fixed that with the forward wings. I believe they produce downward lift though which provides stability at the expense of efficiency.
Lastly; I want to say that the more extra surfaces you see on an aircraft, thats the testament that basic aircraft has relatively more stability and control issues. Though that's not a bad thing on itself if its fixed properly.
Don't want to spark a discussion, but turns out that the most worshipped designs are the flawed ones. Don't believe me; look at P-51 Mustang or F-4 Phantom. :))

A fixed canard does not make an unstable aircraft. It will definitely reduce stability but you need a larger canard to actually make an unstable aircraft.

What is the meaning of this As the AOA increases lift of those front wings would increase also and aircraft would want to pitch up more and go out of control?

So, when the * trailing edge control surfaces* activated or use?

No @Kolom, the front wings (or canards) are not added to the design to fix a CG problem. They are a positive lift producing surface, the goal of this design is to reduce the size of the main wing, thus reducing drag and making the aircraft more efficient. Also, they do not make the aircraft more unstable in pitch. They are designed so that when AOA is increased, they stall before the main wing. That will prevent the aircraft from entering a deep stall. You really should base your answers on solid knowledge, not opinions and/or guesswork.

@Sanchises, I think it depends. With enough moment arm and small static margin it’s possible you end up on the unstable side.

@Jpe61, I agree the second part is a little bit speculative. But without knowing exact location of CG and lift we can only speculate about what we see. On the other hand, idea of reducing drag is interesting. I wonder if they achieved that at all. Earlier stall of the  front wings is a good idea though.

You should really do some reading on the P.180 @Kolom since the design features of the plane are well documented. There is no need for spaculation, the facts are readily available for you, should you choose to spare a moment for them.


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Are there any legal requirements concerning airline pilots and their watches?
Are there any legal requirements concerning airline pilots and their watches? Do they have to be of any particular kind and are pilots required to wear one at all?

Closely related

Not worth an answer but the only thing I can think of is that it can't get in the way of operating the plane. So no Flavor Flav style -- um -- stuff.

Well, a wristwatch can't be used to sneak around the requirement that IFR requires a clock mounted in the aircraft, FAR 91.205(d)(6).  A missing or inoperative clock isn't likely in a modern airliner.  As far as the FAA is concerned, a wristwatch is nothing more than jewelry.
Ages ago, a wristwatch may have helped with calculating fuel burn and range, but even then, it was a convenience rather than mandated equipment.

FWIW, I've had my PPL since the late '70s, and have never owned or worn a wristwatch.

BUT, if you do wear one it has to be a large, blingy, one that leaves no mistake as to your status as a cool dude pilot :)

A pity that we have no rear bumpers to proclaim, my other cessna is a porsche.

@CamilleGoudeseune - "My other plane is a Porsche-Mooney" may be more appropriate... :)